Electronic multiplier



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ELECTRONIC MULTIPLIER 14 Sheets-Sheet l5 O u ST 0 `Q o Nm 1 T IT @mw www www EN am N www n mw n P b n \l Nsm. f www RN n 5151 rlliilillllilll-IIIIL March 16, 1954 Filed sept. s, 1948 INVENTOR Byron .Haz/e//J Y MW ATT RNEY 14 Sheets-Sheet 14 Filed Sept. 5, 1948 INVENTOR Byron wake/75 Y ATTo NEY Patented Mar. 16, 1954 UNITED STATES PATENT OFFICE ELECTRONIC MULTIPLIER Byron L. Havens, Cresskill, N. J., assign'or to International Business Machines Corporation, New York, N. Y., a corporation of New York Application September 3, 1948, Serial No. 47,626

Z Claims.

This invention relates to a computing device and more particularly to a device for computing the product of two quantities.

It is an object of my invention to provide a new and improved device for multiplying two quantities together.

Another object is to provide a, novel electronic device for multiplying two quantities manifested or recorded in the binary system of numerical notation. In the binary system, as is well known, the digital positions in a binary number beginning at the right end digital position and proceeding to the left, correspond in value to the successive increasing powers of 2, that is, 2, 21, 22, 23, etc. Only two kinds of digits are employed in Writing a number in the binary system, namely, a binary 0 and a binary 1. A binary 0 represents zero value at any digital position in the number and a binary 1- represents the power of 2 corresponding to the digital position in which the binary 1 is located. The value of a complete binary number is the sum of the values represented by all of the binary digits. |Thus, a number may be manifested in the binary system by a binary 1 at the digital position corresponding in value to, or at the plurality of digital positions having corresponding values the sum of which equals to, the amount to be manifested with a binary 0 at all other digital positions. Frequently, in manifesting or recording a quantity in the binary system on a record wherein the digital positions are clearly defined, a binary l is indicated by a mark or a perforation at the appropriate digital position while a binary 0 is indicated by the absence of such a marl: or perforation, as the case may be.

A further object of my invention is to provide a novel multiplying device in which two quantities recorded on a record sheet are multiplied and the product is recorded.

Still another object is to provide a new and improved multiplying device in which two quantities, either or both of which is recorded on a record sheet or is manually selected, are multiplied by an electronic circuit device and the product is either recorded or visually indicated,

An ancillary object of my invention is to provide a novel electronic commutator.

Another object is to provide a new circuit arrangement etfective to translate a binary numthe simultaneous occurrence of voltage impulses at three or more different points.

Another object is to provide a new and simplified pulse inverting circuit.

A further object is to provide a novel synchronous delay circuit for voltage impulses.

The adding circuits and the related coincidence circuits disclosed herein are disclosed and claimed in copending divisional application Serial No. 263,731 led December 21, 1951. The commutator and pulse delay circuits disclosed in the present application are disclosed and claimed in copending divisional application Serial 262,732 filed December 2l, 1951.

In accordance with my invention, one of the two quantities to be multiplied, that is the multiplicand, is translated into time coded, voltage impulse form and supplied simultaneously to a plurality of coincidence circuits corresponding to the different digital positions in the multiplier, each coincidence circuit being responsive to the digit in the multiplier in the corresponding digital position. Then, through the action of the coincidence circuits, all or" the digits of the multiplicand are multiplied by each digit of the multiplier individually with each resulting partial product appearing in coded impulse form in the output of the corresponding coincidence circuit, each digit of the multiplicand being simultaneously and individually multiplied by every digit of the multiplier. The partial products thus obtained are then applied to a series chain of adding circuits, known as adding boxes, at different points on the chain corresponding to the proper columnar position of the partial products for adding. The resulting sum represents the product of the multiplicand and the multiplier in time coded impulse form which may be translated into another' form for recording purposes.

Other objects and novel features of the invention are pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle oi the invention and the best mede, which has been contemplated, oi applying that principle.

In the drawings:

Fig. l is a block diagram showing the general relationships between the different components of a multiplying device embodying my invention.

Figs. Zul-gil together comprise a circuit diagram of the multiplying device represented generally in Fig. l.

Fig. 3 is a diagram illustrating the position relationships of Figs. 2ML-j) in forming the complete circuit diagram.

Fig. 4 is a sectional elevation view of a record reading and punching machine suitable for use in the multiplying device.

Fig. 5 is a detailed circuit diagram of an individual adding box as incorporated in Figs. 2h and 2u'.

Fig. 6 illustrates the usual manner of performing the multiplication operation for a sample problem.

Fig. 7 is a diagram illustrating the multiplication operation in the multiplying device for the same sample problem.

General arrangement of multiplying device in the multiplying device as shown in Fig. l, groups oi' switches illu and Illb are arranged to permit alternate use of a record reader or a manual selectorI to introduce the problem and another group of switches idc to permit alternate use of a product recorder or a visual product indicator as desired.

if the record reader and recorder are employed, the record reader reads the problem (i. e., reads the multiplicand and multiplier from a record, such as the familiar perforated record card) and closes, or causes energization of, certain of a plurality of circuits selectively i-n each of two groups of circuits to represent the multiplicand. and multiplier, respectively. After the multiplication operation is' completed, certain circuits extending through the recorder are energized selectively to' represent the product and to cause that product to be recorded, as by periorating a record card.

In the event-it is desired to set up the problem or any part of it manually rather than automatically from a` record and/or to View the product by visual indicating means rather than to record it, the manual selector for the multiplicand. and multiplier and the visual product indicator are used. The manual selector perm-its the selective closing or energization of circuits manually to represent the multiplicand and the multiplier and includes visual indicators to show the number selected for both the multiplicand and the multiplier. The product indicator is arranged so that upon the completion of certain circuits selectively` to represent the product after the multiplication has been performed, a visual indication of that product is provided as byv the selective illumination oi?v a group of lights.

The circuits selectively energizedv by either theA recordreader or the manual selector, as the case may be, and representing the multiplicand, are

coupled to a multiplicand translator. This translator is effective to translate the selectively energized circuits into time coded voltage impulses. A synchronizer is associated with the multiplicand translator to provide a periodic starting voltage impulse and other impulses for synchronization purposes.

In the time code employed in the device illustrated, a particular period of time is assigned to each digital position in the binary number to be represented. The time base necessary in setting up the code is established by the starting impulse from the synchronizer which, in the particular device illustrated, is repeated at periodic inter- The time immediately following a starting impulse includes a plurality of time periods of equal length, each time period corresponding to a digital position in the binary number. The iirst time period following a starting impulse corresponds to the iirst digital position from the right en-d of the binary number; the second time period corresponds to the second digital position from the right end of the number; and so on through all of the time periods. If a voltage impulse occurs in any time period it represents a binary l at the corresponding digital position in the binary number. A binary il at any digital position is represented by the absence of a voltage impulse in the corresponding time period.

n the particular device illustrated time periods of one inicrosecond each are employed and the device is designed to handle a product having a maximum of sixteen binary digits. Consequently, to obtain the maximum speed of operation, the starting impulse is repeated once every sixteen microseconds. In obtaining the sixteen digit product, the device is designed to handle a multiplicand having up to twelve binary digits and a multiplier having up to eight binary digits. Apparatus of a different capacity may, of course, be used if desired.

As indicated, the output of the niultiplicand translator is a series of coded, time spaced voltage impulses representing the multiplicand. This multiplicand in the coded impulse form is applied simultaneously to a plurality of coincidence circuits corresponding' in number to the maximum multiplier digital positions which the device is designed to handle. Thus, there are eight coincidence circuits. Each coincidence circuit corresponds to a different digital position in the multiplier and is connected to the corresponding one of the selectively energized circuits representing the multiplier as provided by either the record reader or the manual selector. The arrangement is such that if a binary 1 is present at` any digital position in the multiplier, the corresponding coincidence circuit passes on the coded impulses representing the multiplicand. On the other hand, those coincidence circuits corresponding to digital positions in the multiplier in which a binary il is present, do not pass on the coded impulses representing the multiplicand. As a result, the coded impulses representing the multiplicand appear at the outputs of only those coincidence circuits for which there is a binary 1 in the multiplier. The output of each coincidence circuit thus represents the partial product of the corresponding digit of the multiplier and all of the digits of the multiplicand.

To add the partial products supplied from the outputs of the coincidence circuits, aseries chain of adding boxes is provided. Each adding box is arranged to accept simultaneously any two binary numbers in coded impulse form and compute` and amazes deliver the sum of these two numbers in the same coded impulse form but delayed by exactly one time period. The synchronizer is also associated with the adding boxes to insure an accurate time delay.

The outputs of the coincidence circuits are connected to the series chain of adding boxes with an adding box interposed between the outputs of successive coincidence circuits. The single time period delay provided by an adding box is thereby employed to provide in effect a column shift between successive partial products in the addition thereof. Thus, the partial product of one digit of the multiplier and all of the digits of the multiplicand, is added to the partial product of the next digit in the multiplier and all of the digits in the multiplica-nd, with an appropriate column shift therebetween. The sum of all of the partial products is obtained from the output of the chain of adding boxes and is supplied to the product translator in the form of time coded impulses delayed one time period with respect to the input to the chain of adding boxes. The product translator changes the product from the coded impulse form to the form of a plurality of selectively energized circuits. These selectively energized circuits are then effective to cause the product to be recorded or to give a visual indication of the product depending upon whether the translator is associated with the recorder or with the indicator.

Record reader and recorder When the problem is to be taken from a rec-ord, such as a perforated record card, and the product is to be recorded, the switches Illa, I (Ib and Itic in Fig. 1 are set in their upper positions. A record yreading and recording machine, such as is shown dlagrammatically in Fig. 2a and in more detail in Fig. 4 and which is more fully shown and described in the patent to C. D. Lake, Re. 21,133, June 2'7, 1939, may be employed. The purpose of the record reader is to read the multiplicand and the multiplier from a record and selectively energize a plurality of circuits in each of two groups in accordance therewith. The recorder is responsive to a group of selectively energized oircuits representing the product to record that product on a record sheet or card.

As previously indicated, the multiplicand and the multiplier may be manifested on a record card in the binary system by a plurality of perforations spaced along a row of digital positions on the card with a perforation representing a binary 1 and the absence of a perforation representing a binary at any digital position. Preferably, the multiplicand is punched in one field of the card and the multiplier in another field but with the digital positions of both the multiplicand and the multiplier in a single row. Thus, a number of problems may be represented on a single card with each row of digital positions containing a separate problem.

In Fig. 4, a plurality of punched record cards II containing the problems to be multiplied may be placed in a hopper I2 at the left of the machine while a plurality of blank product cards I3 on which the product is to be punched are located in a hopper I4 at the center of the machine. With the machine conditioned for operation, a problem card I I and a product card I3 are fed in synchronism from the two hoppers I2 and I4. A pair of gear sectors I5, only one of which is shown, are carried by 'a shaft I6, rotary movement 'of which moves the sectors to move in turn a corresponding card feed picker slide I1 at the bottom of the problem card hopper I2 to cause the picker knife IB carried by the corresponding slide I'I to feed a card II from the bottom of the hopper I2 to a pair of feeding rollers I9 and 20. Similarly, another pair of gear sectors 2I, only one of which is shown, are carried by a shaft 22, rotary movement of which moves the sectors 2I to move in turn a corresponding card feed picker slide 23 at the bottom of the product card hopper I 4 to cause the picker knife 24 carried by that slide 23 to feed a product card I3 to another pair of feeding rollers 25 and 26. The product and the problem cards so fed are moved along concurrently and in synchronism to convey the problem card II to a sensing station and the product card I3 to a punching station.

As shown in Figs. 2a and 4, the sensing station comprises a rst plurality of sensing brushes NMI-I2), a second plurality of sensing brushes 28b(I-8) a contact roller 29 having a conductive surface and a common brush 30 engaging the contact roller. The twelve sensing brushes 21a( I-I 2) correspond to the twelve digital positions available for the multiplicand, and the eight sensing brushes 28b(I-8) correspond to the eight digital positions available for the multiplier. The

`problem card I I passes between the contact roller 29 and the sensing brushes 21a and 28h, the sensing brushes being arranged in a line axially of the roller 29 so that one end of each brush engages the roller except when separated therefrom by ,the card I I which is of insulating material. When a sensing brush coincides with a perforation in the card II, the brush extends through the perioration and engages the contact roller 29. Thus, with the sensing brushes in a line, both the multiplicand and multiplier are sensed simultaneously 40 switches 3l of the machine to the positive terminal of a suitable direct current voltage supply (preferably having a voltage of the order of +40 volts), such as a direct current generator 32 driven .by a suitable motor 33. Consequently, when a perforation is sensed by a sensing brush during operation of the machine, that brush is suddenly connected to the positive voltage terminal. The cam switches 3| are arranged to be closed only when the card is in a correct reading position for sensing by the brushes.

The sensing brushes NaN-i2) for the multiplicand are connected as shown in Fig. 2a to a set of plug hubs 33a(I-I2), respectively, while the sensing brushes 28130-8) for the multiplier are connected to another set of plug hubs 34170-8) respectively. The common brush 3Q is also connected to ground through a resistor 35 and is connected through another resistor 3S to another plug hub 31.

While the problem card I I is passing to the sensing station, as shown in Fig. 4, the product card I3 is passing through rollers 25 and 2G to the punching station. At the punching station, sixteen punches 38e are arranged in a line to be individually actuated by corresponding punch electromagnet S800-I). These electromagnets 39c(I-i6) in Fig. 2a are connected between a volts supply line and individual plug hubs 40c(I-I6). Theyblank product card I3 is provided with product digital" positions and these digital positions are located under the corresponding 16 punches. Then when a punch magnet is energized, the blank product card i3 is perforated by the corresponding punch at the corresponding digital position.

After the sensing of one problem and the punching of the corresponding product, the succeeding problems on the problem card H are sensed in order and their products 'punched in the same order in the product card 3. rThere-- after the problem card Il and the product card I3 pass through rollers 4! and 42, respectively, in Fig. 4, to the stackers 43 and 54, respectively.

Four voltage supply lines are illustrated in the circuit diagram of Figs. 2(a-:i) and are labeled -g-llOV, Bl, B2 and -llOV These voltage supi plies may be obtained from any suitable source and in the device described the biasing supply lines Bi and B2 preferably are '27 volts and -6 Volts, respectively. A voltage line B3 is provided which is energized from a floating supply source i and through the cam operated switches 3l. When the cam switches 3i are open, line B3 is at one value, preferably v i150 volts, assuming switch its: is closed between plug hub 31 and source 25, and when the cam switches 3| are closed, line B3 is at a more positive value, preferably slightly more positive than the -llO volts line.

The switches Ilia, Ib and itc in Fig. 1 comprise a plurality of single pole double throw switches cm-I2), IGbU-t), leed-I6), as shown in Figs. 2c and 2d. Each of switches ia(I-l2) has one contact p'iuggably connected to the corresponding one ci plug hubs 33a(lel2) of the record reader (Fig. 2a), and its pole pluggably connected to the corresponding one of plug hubs iGdG-I2) (Fig. 2c), which are arranged to feed the multiplicand translator. The other contact of each of switches filmt-i2) is plug*- gably connected to the corresponding one of a plurality of plug hubs dimi-l2) in the manual selector (Fig. 2b).

Each of the switches lilou-S) in Fig. 2d has one contact pluggably connected to the correspending one ci plug hubs Sie( i-ol of the record reader in Fig 2a, and its pole connected pluggably to the corresponding one of a plurality of plug hubs mbH-il) (Fig. 2d) which are arranged to feed the coincidence circuits. "ihe other contact of each of switches mbH-ii) is pluggably connected to the corresponding one of a plurality of plug hubs mbH-8)' in the manual selector (Fig. 2b).

Each of switches llic(i-ii) in Fig. 2c has one contact pluggably connected to the corresponding one of plug hubs Miou-It) of the recorder (Fig, 2a) and its pole connected pluggably to the corresponding one of a plurality of plug hubs 5to( l-Il) (Fig. 2c) which are arranged to ce fed from the product translator. other contact of each of switches HBCU-IE) is pluggably connected to the corresponding one ci a plurality of plug hubs SICH-I6 of the indicator (Fig. 2li).

As previously indicated, one contact of the switch Eil (Fig. 2c) is pluggably connected to plug hub 31 of the record reader while its pole is connected to the positive terminal of the B3 floating supply source y4E. 'lhe other contact of switch lila: is pluggably connected to another plug hub 52 in the manual selector (Fig. 2b).

As is pointed out in detail hereinafter, the plug hubs 45cm-I2) and #mbH-9) are connected through resistive circuits to ground and to -ll volts line. Consequently, as the problem card- Il is read with the switches Iliad-I2), mbH-8), IUCN-I6) and i033 in their upper position, the brushes 21a(|-i2) and 2Std-8) sense the perforations in the card for the multiplicand and multiplier, respectively, and when a brush extends through a perforation to engage the contact roller 28, the corresponding circuit through the corresponding one of the switches It is energized. Thus, the circuit through switches 10a( l-l2) and mbH-8) are selectively energized to represent the multiplicand and multiplier, respectively. In these representations, an energized 'circuit represents a binary l and a deenergized circuit represents a binary 0 in the corresponding digital position. The circuits and components in these representations (and in all other places in the drawings) having reference characters containing the designation ai correspond to the rst digital position at the right end of the multiplicand; those containing a? correspond to the second digital position from the right end; and so on through cl2 which corresponds to the twelfth digital position of the multiplicand. The circuits and components having reference characters containing "he designations bi through bil correspond to the iirst through the eighth digital positions from the right end of the multiplier, respectively. The circuits and components having re `erence characters containing the designations ci through clef correspond to the first through the sixteenth digital positions from the right end of the product, respectively.

As is also pointed out in more detail hereinafter, when the product oi the multiplicand and multiplier is determined, the product translator selectively energizes the circuits through switches MoH-id) to energize the corresponding punch magnets Sec( i-it) and punch the product in the product card.

Manual selector and indicator When it is desired to set up a problem manually and to have a visual indication of the product, the switches lila, 10b and illc in Fig. 1 are placed in their lower position to couple the manual selector and indicator with the multiplicand and product translators. The purpose of the manual selector shown in Figs. l and 2b, is to permit manual completion of selected ones of a plurality of circuits in each of two groups of circuits to select the multiplicand and the multipler. IThe purpose of the product indicator is to provide a visual, easily read indication of the product as determined by the device.

Since the apparatus is designed for use with a multiplicand having up to twelve binary digits, twelve manually operable switches EMU-i2) (Fig. 2b) are provided in the manual selector, corresponding to the twelve digital positions for the multiplicand. Each of the switches 53a- (i-IZ) is connected in series with an individual resistor 54e( i-I2) between the +110 volts supply line and the corresponding one of plug hubs Mad-l2). lTwelve multiplicand indicator lights 55a(!|2), such as incandescent lights, are also provided, with each light corresponding to a different digital position. Each of these multiplicand indicator lights 5MM-i2) is connected between the ground and the side of the corresponding one of the selector switches 53a(!i2) Which is remote from the volts supply line. Thus, when the switches NaN-I2) in Fig. 2d are in their lower position, the closure o f any one of the multiplicand selector switches 53a(l|2) completes the corresponding circuit from the +110 volts supply line through the corresponding one of resistors 53a(||2) and plug hubs "aU-I2) and in addition completes the corresponding circuit from the +110 volts supply line through the corresponding one of indicator lights 55a( I-I2) to the ground. Thus, the closure of any one or combination of selector switches 53a( I-I 2) and the illumination of the corresponding indicator lights 55a(l-I2) then represents a binary 1 in the corresponding digital positions of the multiplicand. An open selector switch 53a(|-|2) and a corresponding non-illuminated indicator light 55a(||2) represents a binary 0 in the corresponding digital position of the multiplicand.

Similarly, eight manual switches 562)(1-8) are provided in Fig. 2b corresponding to the eight digital positions in the multiplier. Each of the multiplier selector switches 56h( I-8) is connected in series with a corresponding one of eight resistors 51b(|8) between the +110 volts supply line and the corresponding one of plug hubs 49130-8). Eight additional indicator lights 58h( I-8) are also provided to represent the multiplier and each is connected between the ground and the side of the corresponding multiplier selector switch 58b(|8) which is remote from the +110 volt supply line. Thus, when switches lb(I-8) in Fig. 2d are in their lower positions, closure of any one of the multiplier selector switches 56b(|8) in Fig. 2b then completes a circuit from the +110 volts supply line through the corresponding one of resistors 51b(l8) and plug hubs 49b(|8), and also causes the corresponding one of indicator lights 58b(l8) to be illuminated representing a binary 1 in the corresponding digital position of the multiplier.

To indicate the product of the multiplicand and the multiplier, sixteen more indicator lights 59c(|-|6) are provided in Fig. 2b, each corresponding to a different digital position of the product. Each of the product indicator lights 58c(||6) is connected in series with a corresponding one of sixteen resistors 60c(l-|6) between the +110 volts supply line and the corresponding one of plug hubs Ic( I-IG). When the product is determined by the multiplying device, the circuits through those product indicator lights corresponding to the digital position in the product at which a binary 1 appears, are completed and the illuminated lights provide an easily read visual indication of the product.

The multiplicand translator 'Ihe function of the multiplicand translator (Figs. l, 2c, 2e, 2f) is to receive the multiplicand in the form of a binary number represented as a plurality of selectively energized circuits and to generate time coded voltage impulses corresponding to that number.

As previously indicated, in the time code employed in the multiplicand translator, the first microsecond time period following a starting impulse corresponds to the first digital position from the right end of the binary` number to be represented; the second microsecond corresponds to the second digital position; the third microsecond corresponds to the third digital position, and so on through the y twelve digits which may be handled by this apparatus. A voltage impulse in any particular microsecond represents a binary l in thecorresponding digital position while the absence of vanimpulse in any microsecond time period represents a binary 0.

In the multiplicand translator, twelve resistive voltage dividers Glad-I2) corresponding to the twelve digital positions available for the multiplicand, are connected between the -110 volts supply line and the ground as shown in Fig. 2c. Each of the plug hubs 46a(|-|2) which are pluggably connected to either the record reader or the manual selector through switches Iliad-I2) is also connected to an intermediate tap 62 on the corresponding divider Glad-I2). A second intermediate tap 63 on each divider `[HMI-I2) between the first tap 62 and the 110 Volts supply line is connected by the corresponding one of twelve lead wires Mad-I2) to the translator proper of Figs. 2e and 2f. It is then evident that each second tap 63 and the corresponding one of lead wires 64a(l|2) may be at one of two voltages. So long as the corresponding one of the sensing brushes 21a(|-i2) in the record reader (Fig. 2a) does not sense a perforation in the problem card or the corresponding one of selector switches 53a in the manual selector (Fig. 2b) is not closed, depending upon whether the record reader or the manual selector is to be controlling, the second tap 63 and its associated lead wire are at their more negative voltage. When a sensing brush senses a perforation or when a selector switch is closed, as the case may be, the voltage of the rst intermediate tap 62 on the corresponding divider Sla is made considerably more positive to cause in turn the second tap 63 and its associated lead wire 64a(||2) to become more positive.

The translator proper includes a multi-stage electronic commutator 65-80, in the left-hand half of Figs. 2e and 2f, which is actually a part of the product translator as well as the multiplicand translator, and twelve switching circuits 8|a(||2), in the center of Figs. 2e and 2f, corresponding to the twelve digital positions, respectively, available for the multiplicand. The commutator -80 has sixteen stages, the rst twelve of which 65-16 are associated with the twelve switching circuits 8la(I-I2), respectively, for use in translation of the multiplicand, while all sixteen stages are associated with the product translator which can accommodate a sixteen digit product. A starting impulse is received from the synchronizer indicated in Fig. 1 at the rst stage 65 of the commutator in the lower left-hand corner of Fig. 2f and that impulse is passed along from stage to stage at a rate of one time period, that is, one microsecond, per stage.

Each commutator stage (Figs. 2e and 2f) comprises a pentode 82, such as a. Western Electric 6AK5 tube and a triode 83, preferably half of a twin triode such as a Western Electric 2C51 tube, and their associated circuits. The anode of the pentode 82 is connected to the +110 volts supply line through a resistor 84 and an inductor 85. A condenser 86 is connected from the anode of the pentode 82 to the ground. The cathode of the pentode 82 is connected to the ground; the suppressor grid is connected to the cathode; and the screen grid is connected to the +110 volts supply line. The control grid of the pentode 82 of the first stage 65 of the commutator is connected through a resistor 81 to the :biasing voltage line B2 and also through a coupling condenser 88 to a coaxial line 88 through which the starting impulse is delivered. The control grid of each of the pentodes 82 of the other stages is connected to the cathode of the triode 83 of the next lower stage arranged in a cathode follower circuit.

The output of each pentode 82 of the commutator 65-80 is delivered to the corresponding triode 83 by a coupling from the `anode of the pentode y82 to the control grid of the triode through a coupling condenser il@ and a "first diode Si, preferably a germanium crystal diode, such as a Sylvania 1N34 crystal, which oifers its lower impedance to current flow toward the grid. The junction point between the coupling condenser 190 and the nrst diode 9| is connected through a resistor S2 to the -110 volts supply line. rThis same junction point is also connected through a second diode 93, also preferably a germanium crystal diode, to the biasing supply line B with the diode 93 offering its lower impedance to current now toward the biasing line B2. rThe saine junction point is further connected through a third diode 94, also preferably a germanium crystal diode, to the biasing voltage line Bl, with the third diode 94 offering its higher impedance to current flow toward the biasing line BI. The control grid of each triode Vi3 is also coupled Vby a condenser 95 to a synchronous impulse supply line S! which is connected to the synchronizer to be later described. The triode control grid is also connected through a, fourth diode 96, also preferably a germanium crystal diode, and a, resister Si in series therewith, to a clamp impulse supply line KI, which is connected to the synchronizer, with the fourth diode offering its lower impedance to currentow toward the clamp supply line Kl. The anode of each triode 83 is connected through a resistor S8 to the +1191 volts supply line while the cathode is connected to the -110 volts supply line through a load resistor 89 in a cathode follower circuit which differs somewhat from the conventional cathode follower in that the cathode is tied to a point substantially negative with respect to the grid return circuits. This permits impulses to be transmitted more readily by the cathode follower.

A positive rectangular, low impedance, syn chronous voltage impulse is to be supplied through the synchronous impulse line Si from the synchronizer once each time period; that is, once each microsecond. This synchronous impulse is arranged to be approximately one-third of a microsecond in duration and a starting impulse is arranged to occur simultaneously with every six teenth synchronous impulse. Conincident with the termination of each synchronous impulse, a negative voltage impulse having a steep wave front is supplied through the clamp line Kl from the synchronizer. The function and relative magnitudes of the synchronous and clamp impulses are described hereinafter in the discussion of the operation of the commutator.

The circuit arrangement, including the pentode triode S3 and diodes ill, 93, Bil and 95, in each commutator stage, as just described, constitutes a synchronous pulse delay circuit.l Considering, for example, any given one of commuu tator stages S5-8t (Fig. 2f), let it be assumed that the grid of triode se is originally at the potcntial ci supply line Bl and condenser S5 is charged to the difference between the voltage of line El and the voltage of line Si. Now, because of the connection of the -ll volts line through resistor to the junction between the condenser and the rst diode 9i, that junction tends to highly negative. However, the connection of the timid diode Sri prevents the junction from being more negative than biasing line B! which in this'particular arrangement may be about 27 volts. "Sie third and first diodes together also prevent the grid of the triode 83 from becoming "12 more negative kthan biasing bline Bl. :It is then evident that while the pentode 82 is nonconductive, the condenser su, coupling the anode oi the pentode'? to the control grid of the triode is charged to the voltage difference between the -i-llo volts supply line and the biasing line Bl. When a positive impulse is impressed on the control grid of the pentode 82, -it becomes conductive and the voltage at its anode drops. The coupling condenser 9B Athen discharges but its tere minal remote from the pentode 82 necessarily remains at the voltage level of the biasing line Bi. At the termination of the positive impulse at the grid, the pentode 8,2 again becomes non'- conductive and the voltage of itsanode rises. As a result, a positive voltage impulse is passed through the coupling condenser Se and the first diode el tothe grid of the triode S3 and also to the condenser $5. I'owever, through the action of the second diode y9 3, the maximum voltage of the positive impulse thus delivered to the grid of the triode 83 is limited to the voltage level of the biasing line B2, which level is more positive than that of biasing line BL Although the duration of the positive impulse passed through the coupling 4condenser Sil is rela tively short, it changes the charge on the condenser coupling the grid of the triode to the synchronous impulse line Si to establish the grid at the level of line B2. rlhe purpose of the first diode 9| is to permit the `voltage of the terminal of the coupling condenser 93 which is remote from the pentode-SQ to Vreturn to the level of biasing line Bi without removing such charge from the con-- denser and altering the voltage of the grid of the triode 3. The tendency of the remote terminal of the coupling condenser 9D to return to the level of line Bi is the result of the combination of two effects, one being the second overshoot ci' the anode pulse of the'pentode 52 and the other being the action of the resistor G2 connecting 'that terminal to the volts supply lei-ne. lf this remote terminal has not completely returned to the level of 'line Bi by the time the next clamp impulse occurs, the return is completed by that clamp impulse, It is kdesirable that the remote terminal of the condenser 9D be substantially ren turned to the level of line Bl before the next clamp impulse occurs, for if the return is accom- In, plished primarily `by the clamp impulse, a spurious negative impulse is generated in 4the anode circuit of pentode 82, which is obviously undesirable.

From the foregoing, it is evident that if he pentode 32 of the given stage remains non-conductive, the grid of the triode 83 is at `the voltage level of biasing line Bl. However, when the pentode 82 becomes conductive as the result of a positive impulse on its grid, -a voltage pedestal is estab lished on the grid of the triode 83 of the same stage at the level of biasing line B2. The con stants of the load circuit of the pentode 32 are chosen to give the optimum wave shape for establishing the pedestal. It is to be noted that the voltage pedestal is established as a result of the pentode 182 becoming non-conductive rather than as a result of the pentode becoming conductive upon application of the positive impulse on its grid.

The magnitude of a synchronous impulse on line Si is such that if the grid of the triode 83 in the given commutator stage is at the vvoltage level of biasing line gBl, prior to the synchronous impulse, the impulse produced at the cathode of triode 83 will not raise the voltage ofthe control grid 

